1. Field of Technology
The present invention relates to an automatic focusing device for any interchangeable lens assembly having no auto-focusing function.
The present invention also relates to an automatic exposure control device for enabling an exposure control function to effect an automatic exposure control regardless of the type of a photo-taking optical system, that is, when a photo-taking optical system adaptable to a full aperture metering and exposure calculating means is mounted, or when a photo-taking optical system not adaptable to the full aperture metering and exposure calculating means is mounted, or when a photo-taking optical system other than the above mentioned two photo-taking optical systems is mounted.
2. Description of the Prior Art
As is well known to those skilled in the art, a lens-interchangeable camera system having an automatic focusing capability now commercially available is such that the automatic focusing capability does not work when any interchangeable lens assembly inadaptable to the automatic focusing capability of such camera system is mounted on such camera system.
Moreover, when an aperture control system in a lens assembly is changed, an automatic aperture presetting capability (an automatic aperture control) does not work, also.
In view of the foregoing, a system has been proposed wherein a convertor is interposed between a camera body and any interchangeable lens assembly inadaptable to the automatic focusing capability to make the automatic focusing capability work very well, such as disclosed in, for example, the Japanese Laid-open Patent Publications No. 58-098711, No. 58-098712, and No. 58-114008.
The Japanese Laid-open Pat. Publication No. 59-140408 discloses a system wherein the automatic focusing capability can work only when data read from an interchangeable lens assembly are acceptable to the camera system, but cannot work when they are not acceptable to the camera system. The Japanese Laid-open Pat. Publication No. 58-211127 discloses a system wherein the full aperture metering and exposure calculating means can work only when data read from an interchangeable lens assembly are acceptable to the camera system, but an actual aperture metering and exposure calculating capability can work when they are not acceptable to the camera system.
It has, however, been found that the prior art systems disclosed in the Japanese Laid-open Pat. Publications No. 58-098711, No. 58-098712 and No. 58-114008 have numerous problems which will now be discussed. More specifically, according to these prior art patent literatures, much attention is centered on the automatic focus detecting function, and no automatic exposure control (aperture control) is taken into consideration. Therefore, even though the convertor referred to above is used, an automatic exposure control operation cannot take place when the aperture control system is changed.
Apart from the above, a system has not yet been made available wherein both the automatic focusing capability and the exposure control capability are enabled even if an interchangeable lens assembly having a photo-taking optical system inadaptable to the full aperture metering and exposure calculating means is mounted.
In summary, the prior art systems wherein the photo-taking optical system inadaptable to the full aperture metering and exposure calculating means is mounted with the intervention of the convertor are insufficient in respect of function, which largely limits the available types of optical systems.
Furthermore the prior art automatic focusing system has the following problems. Specifically, the system is so designed as to detect a front focus condition, a rear focus condition and an in-focus condition, and does not perform an automatic focus adjustment by calculating beforehand the amount through which a convertor lens is to be moved. In other words, since based on a detection data condition or the in-focus condition the convertor lens is moved on a feedback control scheme, it often happens that the lens undergoes a hunting. In order to avoid the occurrence of the hunting of the convertor lens, the speed of movement of the convertor lens (the focusing speed) has to be lowered.
Moreover, despite the fact that a focus detecting unit provided in the camera body is capable of determining a defocus amount, all of the available functions capable of being performed by the focus detecting unit cannot be fully utilized to advantage with the speed of movement of the convertor lens (the focusing speed) set to a low value, because nothing other than information representative of the front focus condition, the rear focus condition and the in-focus condition is utilized for the automatic focus adjustment.
This is due to the fact that the defocus amount and the focusing amount of the convertor lens have no linear relationship with respect to each other and, therefore, no accurate focusing amount can be determined.
Furthermore, the distance to a target object to be photographed is so varied that only the movement of the convertor lens would not always bring the target object into the desired in-focus condition. If the focusing is insufficient only by means of the automatic movement of the converter lens, the interchangeable lens assembly must also be moved manually for a complete focus adjustment.
Although the automatic focusing device is going to perform the automatic focus adjustment by moving the convertor lens, the convertor lens would be brought to one of the opposite limit positions between which it can move, in the event that the distance to the target object is such that the target object cannot be focused only by the movement of the convertor lens used in an AF convertor.
According to the prior art automatic focusing device such as disclosed in the Japanese Laid-open Patent No. 58-098711, when the convertor lens is brought to one of the opposite limit positions, a position detecting switch is closed to effect a warning that the automatic focus adjustment cannot be accomplished only by the movement of the convertor lens.
In other words, a decision to determine if the distance to the target object is such that the automatic focus adjustment cannot be accomplished only by the movement of the convertor lens cannot be made before the actual movement of the converter lens, but done only when and after the converter lens is actually brought to one of the opposite limit position to cause the warning.
In view of the foregoing, a quick decision cannot be made to determine if the additional manual focus adjustment is to be needed in the interchangeable lens assembly, and therefore, a quick focus adjustment cannot be carried out.